Comparative biodistribution of three Ga-67 labeled MoAb T101-chelator conjugates was performed in mice to evaluate their in vivo stability. MoAb T101 (IgG2) was conjugated with three chelators; two derivatives of 1,4,7-triazacyclononane triacetic acids with p-isothiocyanatobenzyl group (p-SCN-Bz) substituted at an ethylene backbone (C-NOTA) or p-SCN- phenylethyl group substituted at alpha position of a carboxylic acid (N- NOTA), and 2-p-SCN-Bz-6-methyl diethylenetriamine pentaacetic acid (1B4M) and then radiolabeled with Ga-67. Normal mice were co-injected with each Ga-67 conjugate and an equal dose of I-125 T101 as a control, and sacrificed in groups of five up to 120 hr postinjection. The three Ga-67 conjugates showed different biodistributions especially in blood and bone. The Ga-67 C-NOTA conjugate was retained in the blood the longest with 16.3% ID/g remaining at 120 hr, during which accumulation in the bone was 2.7% ID/g. For the N-NOTA, the corresponding blood activity was 10.8% ID/g and the bone activity was 7.4% ID/g. In contrast, the Ga- 67 1B4M conjugate cleared from the blood rapidly with 4.9% ID/g at 24 hr and accumulated rapidly in the bone with 15.9% ID/g. The bone to blood ratio increased from 0.07 to 0.17 for the C-NOTA, 0.18 to 0.45 for the N- NOTA, and 3 to 76 for the 1B4M between 6 and 120 hr. The bone uptake was inversely correlated to serum stability of the corresponding Ga-67 chelates in vitro. The inverse relationship between the blood and bone activity appears to indicate that the bone uptake was related to the dissociation of Ga-67 from the chelates. The whole body clearance and the retention of the Ga-67 C-NOTA conjugate in the blood and bone were similar to those of I-125 labeled T101, suggesting that the C-NOTA does not release Ga-67 to serum or intracellular proteins appreciably. This study suggests that the Ga C-NOTA complex is stable in vivo and the C-NOTA conjugate is suitable for complexing Ga-67, Ga-68 and Ga-66 for tumor diagnosis and therapy.